The present invention relates generally to an image processing apparatus, and more particularly to an image processing apparatus for carrying out a shadow process to automatically add a shadow to an image, which apparatus is applicable to a digital copier, a printer or the like.
In an image processing system, several image decorating functions are used. For example, a shadow process is one of such functions, and the shadow process is carried out so that a composite image of the original image with its shadow is output. FIGS. 2A and 2B show two typical shadow processes, one being called a solid shadow process and the other being called a plane shadow process. In FIG. 2A, the solid shadow process is carried out, and the original image is accompanied by three transitive images as the shadow images. A composite image of the original image and the shadow images is formed, so that it looks as if the original image was moved to the right diagonally downward with the traces of the image movement remaining there. In FIG. 2B, a plane shadow process is carried out, and a shadow image is formed at a desired position to which the image is moved to the right diagonally downward by a displacement (=3) equivalent to the movement of the image in the solid shadow process and a shadow is cast from the original image onto the position. A composite image of the original image and the shadow with shadow portions being cast onto the position of the shadow is formed in the plane shadow process.
Conventionally, such movement of the image in the shadow process is carried out by moving binary data by means of a thickening or spreading circuit for carrying out a spreading process and a thinning or choking circuit for carrying out a choking process. FIG. 1 shows a line memory used in each of such circuits. This line memory 1 has data input ports D0in through Dm-1in and data output ports D0out through Dm-1out. Control signals input to the line memory 1 are a pixel clock CLK, a read clock RDCLK, a write clock WRCLK, a write enable signal WE, a read enable signal RE, a line sync signal LSYNC, a reset write signal RSTW, and a reset read signal RSTR. It is required that the line memory has a large storage capacity and a high-speed data access.
In FIG. 1, reference numerals 2a and 2b denote registers (D flip-flop) R0 and R1 coupled to the line memory 1 via the data input ports and the data output ports. Similarly, registers R2 through Rm-1 are coupled to the line memory 1 via the data input and output ports. Reference numeral 3 denotes a logic element serving as a selector for selecting a line from a set of lines ("m": the number of lines).
Input data Din is supplied to the line memory 1 via the data input port D0in. The data output port D0out of the line memory 1 is connected to the input of the register R0, and the output of the register R0 is connected to the data input port D1in and connected to the logic element 3 for transferring the data from the port D0in to the port D1in (or the logic element 3). This data transfer procedure is repeatedly carried out with respect to the data input ports D1in through Dm-1in so that the image is moved to an arbitrary position to the right diagonally downward by a displacement corresponding to the selected number "m-1" of the lines. By selecting a line from the number "m" of the lines by means of the logic element 3, it is possible to move the image to a arbitrary position to the right diagonally downward.
In a conventional image processing apparatus, such as a digital copier, which performs real-time operations with no frame memory, a shadow outlining process is carried out by storing several lines of image data in several line memories. When the plane shadow process is carried out, an arbitrary line of the image data from the line memories is selected for shadow image data in the plane shadow process. However, there is a problem in that if the above mentioned shadow process is carried out a shadow may be added to an image of undesired matter such as dust or stain in the original image. Thus, it is necessary to remove the undesired matter such as dust or stain from the original document before a shadow process is carried out.